Martin Theuring

Comparison of Ag and SiO2 Nanoparticles for Light Trapping Applications in Silicon Thin Film Solar Cells.

Plasmonic and photonic light trapping structures can significantly improve the efficiency of solar cells. This work presents an experimental and computational comparison of identically shaped metallic (Ag) and nonmetallic (SiO2) nanoparticles integrated to the back contact of amorphous silicon solar cells. Our results show comparable performance for both samples, suggesting that minor influence arises from the nanoparticle material. Particularly, no additional beneficial effect of the plasmonic features due to metallic nanoparticles could be observed.

Laser perforated ultrathin metal films for transparent electrode applications

Transmittance and conductivity are the key requirements for transparent electrodes. Many optoelectronic applications require additional features such as mechanical flexibility and cost-efficient fabrication at low temperatures. Here we demonstrate a simple method to fabricate high performance transparent electrodes that is based on perforation of thin silver layers using picosecond laser pulses. Transparent electrodes have been characterized optically and electrically in order to determine the influence of specific surface coverage. Special attention was paid to maintaining sufficient conductivity in the metal-free areas. As a result, transmittance of a much higher bandwidth was achieved as compared to unpatterned metal films. Transparent electrodes have been fabricated on glass and plastic foil, as well as wafer-based silicon heterojunction solar cells, demonstrating their applicability for most relevant cases.

Spectral and temporal multiplexing for multispectral fluorescence and reflectance imaging using two color sensors

Fluorescence imaging can reveal functional, anatomical or pathological features of high interest in medical interventions. We present a novel method to record and display in video rate multispectral color and fluorescence images over the visible and near infrared range. The fast acquisition in multiple channels is achieved through a combination of spectral and temporal multiplexing in a system with two standard color sensors. Accurate color reproduction and high fluorescence unmixing performance are experimentally demonstrated with a prototype system in a challenging imaging scenario. Through spectral simulation and optimization we show that the system is sensitive to all dyes emitting in the visible and near infrared region without changing filters and that the SNR of multiple unmixed components can be kept high if parameters are chosen well. We propose a sensitive per-pixel metric of unmixing quality in a single image based on noise propagation and present a method to visualize the high-dimensional data in a 2D graph, where up to three fluorescent components can be distinguished and segmented.

Simultaneous Color Imaging and Fluorescence Detection using a Single Camera Sensor

We demonstrate an imaging system intended for medical applications that allows to display simultaneously and in real-time both the reflectance image as well as the signal from up to three fluorescent dyes.

Computational investigation of silicon thin-film solar cells withgrating structures fabricated by holographic lithography

Light trapping due to rough interfaces is a common and industrially applied technique to enhance cell performance in silicon thin-film solar cells. The induced scattering enhances the absorption and consequently the conversion efficiency of the device. Periodic structures promise to further enhance the light trapping, allowing a beneficial reduction of the absorber layer thickness. In this work, solar cells with transparent front contacts with a two-dimensional (2D) grating structure produced by holographic lithography are investigated. The grating structures are characterized by various means and the results are used to calibrate finite-difference time-domain (FDTD) simulations. With the computational method, the influence of the grating height on the solar cell performance is investigated.